One common type of container package comprises a container closure having a base wall and a peripheral wall, commonly made of metal or plastic, which has a gasket of vinyl plastisol cast in situ and extending along the peripheral wall and at least a portion of the base wall to overlie the end of the container. Such a closure is applied by forcing it axially onto a container having threads and the threads on the container deform the gasket by indentation of the container threads into the gasket so that when the gasket is rotated counterclockwise relative to the containers, the closure is removed to provide access to the contents.
One common problem with respect to such packages of a container and closure is that the packages are subjected to cold flow of the gasket material during the shelf life on the package which may comprise two to three years. In the prior art designs, the gasket has uniform thickness around the periphery of the closure and there is a tendency for the gasket material to produce high compressive stresses which result in high removal torques. The removal torques increase as the shelf life of the package increases.
Another problem that occurs where the contents being packaged are hot is the tendency of the hot gases in the head space above the contents to cause a high pressure tending to force the closure off the container at least until the container cools.
In U.S. Pat. No. 3,371,813, it is proposed to provide circumferentially spaced and radially extending ribs on the gasket which are tapered radially inwardly toward the top panel of the closure and engage the threads on the container. Such ribs function to decrease the removal torque by reducing the area of contact but are difficult to form and control.
Accordingly, among the objectives of the present invention are to provide a closure wherein highly stressed areas can be relaxed resulting in lower removal torques; wherein the hot gases can be vented during application of the closure to prevent the pressure from forcing the closure off the container; and wherein the areas of the thread contacting surfaces of the gasket are easily controlled.
In accordance with the invention, the container closure is adapted to be applied to a container having threads by an axial movement and to be removed by a rotary movement to open the container comprising a body including a base wall and a peripheral wall and a gasket of plastic material formed in situ along the peripheral wall and at least a portion of the base wall which is adapted to overlie the end of the container. The surface of an annular portion of the gasket along the peripheral wall is formed with a plurality of circumferentially extending substantially flat surfaces such that it has a polygonal configuration in transverse cross section with axially extending channels at the junctures of the substantially flat surfaces. When the closure is applied to the container, the threads on the container deform the surfaces of the polygonal portion by indentation to define complementary threads therein. When the closure is being applied, the channels permit gases in the head space of the container to escape so that excessive pressurization tending to force the cap off does not occur. After the closure is applied to the container, the channels provide areas into which the plastic material may cold flow to release excessive compressive stresses which develop during shelf life of the package comprising the closure and container, thereby resulting in lower removal torques.